1. Field of the Invention
The present invention relates to a biodegradable resin composition, which has similar properties as that of conventional plastics, but upon disposal, is decomposable by ordinary microorganisms existing in the environment. The present invention also relates to a filler for a biodegradable resin composition, which is suitably used for the biodegradable resin composition of the present invention, and has an excellent decomposability. Further, the present invention relates to a molded article formed of the biodegradable resin composition of the present invention, which is suitably used as a housing and the like for various electric products, and is easily disposable without causing any environmental pollutions.
2. Description of the Related Art
Conventionally, resin compositions are used for various electric products as housings thereof and the like. However, the resin compositions damage incinerators by the heat generated during combustion, and discharge toxic gases such as dioxin and the like, when they are combusted for disposal. Moreover, the resin compositions are hardly decomposed when they are buried in the soil. The resin compositions hence have problems in that they cannot be easily disposed and they may cause environmental pollutions.
In April 2001, the “Home Appliance Recycling law” was enacted. Due to this law, large electric products, such as TV (television) and the like, have been recovered upon disposal. However, the collected large electric products are rarely reused. Further, most large electric products are still disposed as incombustible wastes because there is no legal punishment to the offender by the above-mentioned law. In the case of small electric products, the number of sales is much larger than that of the large electric products, so that an enormous amount of incombustible waste are generated as a result. Accordingly, disposal of electric products, regardless of large or small, has become a serious social problem.
Recently, biodegradable resins have been focused as the solution of the above-mentioned problem. The term, “biodegradable resins” refers to the resins which are decomposed into low molecular weight compounds after disposal, and in the end, decomposed to water and carbon dioxide, by microorganisms in the environment (Biodegradable Plastics Society, ISO/TC-207/SC3). The biodegradable resins are roughly distinguished into three types: one having aliphatic polyester resin in a molecular skeleton thereof; one having polyvinyl alcohol; and one having polysaccharides. For their utilization, the biodegradable resins have been developed to realize mainly disposable products, such as materials for agriculture, forestry and marine industry (e.g., films, plant pots, fish lines and fish nets), materials for civil engineering work (e.g., water-holding sheets, plant nets and the like), packages and containers (e.g., those that are difficult to recycle due to soils, foods and the like attached thereto) and the like.
As has been mentioned above, use of the biodegradable resin for a resin composition enables disposal into the soil and the like, and remarkably reduced possible hazard to the environment.
In the case that the biodegradable resins are utilized for molding articles of electric products such as housings, structural materials and the like, however, the biodegradable resins themselves do not have desirable physical properties for the electric products, namely excellent physical properties such as strength, thermal resistance, flame retardancy and the like. For example, aliphatic polyester resins, one type of biodegradable resins, have glass transition temperature (Tg: the temperature where storage elastic modulus is reduced in about 1/10 to 1/100 relative to the storage elastic modulus at ordinary temperature) of approximately 60° C., the storage elastic modulus is therefore rapidly reduced to approximately 1×107 Pa at the temperature above 60° C., from the storage elastic modulus of 1×109 Pa at ordinary temperature. Accordingly, deformations of aliphatic polyester resins tend to easily occur above 60° C. Owing to this reason, single use of aliphatic polyester resins for housings of electric products is not acceptable.
A resin composition is therefore desired that provides excellent physical properties to conventional plastics, for example, strength, water-resistance, molding workability and flame retardancy during use, rapid decomposability by ordinary microorganisms existed in the environment after disposal, and suitability for molding articles of various electric products and the like.